MEF2C and CEBPA: Possible co-regulators in chronic myeloid leukemia disease progression

Silencing of lncRNA KLF3-AS1 represses cell growth in osteosarcoma via miR-338-3p/MEF2C axis

BACKGROUND

Osteosarcoma (OS) is a highly recurrent malignancy occurring among adolescents. The goal of this research was to scrutinize the role and action mechanism of KLF3-AS1 in OS.

METHODS

Western blotting and quantitative reverse transcription real-time PCR were conducted to ascertain the mRNA expressions of miR-338-3p, KLF3-AS1, and MEF2C in OS cell lines and tissue samples. Colony formation and CCK-8 experiments were done to evaluate the proliferative capacity of the cells. Western blotting was also executed to measure the relative expressions of the proteins Bcl-2 and Bax. RNA immunoprecipitation and dual luciferase reporter experiments were carried out to validate the target relationships among MEF2C, KLF3-AS1, and miR-338-3p. Mouse xenograft models were created to assess the influences of KLF3-AS1 on the growth of tumors in vivo.

RESULTS

Elevated levels of KLF3-AS1 and MEF2C and reduced amounts of miR-338-3p were identified in OS. KLF3-AS1 targeted miR-338-3p, and miR-338-3p further targeted MEF2C. Silencing KLF3-AS1 induced apoptosis and attenuated proliferation in vitro and repressed the tumor growth in vivo. Inhibiting miR-338-3p inverted the cancer-suppressing effects of KLF3-AS1 silencing. Meanwhile, loss of MEF2C partially eliminated the effects brought about by miR-338-3p downregulation, namely the stimulation of cell growth and suppression of apoptosis.

CONCLUSIONS

Silencing of KLF3-AS1 could repress the growth of cells and induce apoptosis by regulating miR-338-3p/MEF2C in OS. This suggests that the regulatory axis KLF3-AS1/miR-338-3p/MEF2C is a prospective target for OS treatment.

Regulation of human T-cell leukemia virus type 1 antisense promoter by myocyte enhancer factor-2C in the context of adult T-cell leukemia and lymphoma

Adult T-cell leukemia and lymphoma (ATLL) is an intractable T-cell neoplasia caused by a retrovirus, namely human T-cell leukemia virus type 1 (HTLV-1). Patients suffering from ATLL present a poor prognosis and have a dearth of treatment options. In contrast to the sporadic expression of viral transactivator protein Tax present at the 5' promoter region long terminal repeats (LTR), HTLV-1 bZIP gene (HBZ) is encoded by 3'LTR (the antisense promoter) and maintains its constant expression in ATLL cells and patients. The antisense promoter is associated with selective retroviral gene expression and has been an understudied phenomenon. Herein, we delineate the activity of transcription factor MEF (myocyte enhancer factor)-2 family members, which were found to be enriched at the 3'LTR and play an important role in the pathogenesis of ATLL. Of the four MEF isoforms (A to D), MEF-2A and 2C were highly overexpressed in a wide array of ATLL cell lines and in acute ATLL patients. The activity of MEF-2 isoforms were determined by knockdown experiments that led to decreased cell proliferation and regulated cell cycle progression. High enrichment of MEF-2C was observed at the 3'LTR along with cofactors Menin and JunD resulting in binding of MEF-2C to HBZ at this region. Chemical inhibition of MEF-2 proteins resulted in the cytotoxicity of ATLL cells in vitro and reduction of proviral load in a humanized mouse model. Taken together, this study provides a novel mechanism of 3'LTR regulation and establishes MEF-2 signaling a potential target for therapeutic intervention for ATLL.

2-Methoxyestradiol combined with ascorbic acid facilitates the apoptosis of chronic myeloid leukemia cells via the microRNA-223/Fms-like tyrosine kinase 3/phosphatidylinositol-3 kinase/protein kinase B axis

Chronic myeloid leukemia (CML) is a malignant myeloproliferative tumor. 2-Methoxyestradiol (2-ME) is an endogenous estrogen metabolite that shows efficacy in human malignancies. Ascorbic acid (AA) possesses antioxidant activity. This study explored the mechanism of 2-ME combined with AA in the apoptosis of CML cells. Firstly, human CML cell lines were treated with 2-ME and AA. The cell viability, apoptosis, reactive oxygen species (ROS), and mitochondrial membrane potential (MMP) were detected. miR-223 expression in CML cells was detected. In addition, CML cells were transfected with miR-223 inhibitor. The binding relationship between miR-223 and FLT3 was verified. Subsequently, the FLT3 was overexpressed or silenced for the function rescue experiment to confirm the role of FLT3 in CML cell apoptosis. The expression levels of key factors of the PI3K/AKT pathway were detected. Finally, xenograft nude mouse models were established for in vivo verification. 2-ME + AA treatment inhibited CML cell viability and promoted apoptosis, elevated ROS content, and reduced MMP. 2-ME + AA treatment promoted miR-223 expression in CML cells. miR-223 targeted FLT3. Moreover, miR-223 inhibitor or FLT3 overexpression partially annulled the effect of 2-ME + AA on CML cells. 2-ME + AA inhibited the PI3K/AKT pathway via the miR-223/FLT3 axis. Furthermore, 2-ME + AA suppressed CML xenograft growth in mice. Collectively, 2-ME + AA promoted miR-223 expression and suppressed FLT3 and the PI3K/AKT pathway, thereby facilitating the apoptosis of CML cells and inhibiting CML xenograft growth in mice.

Epigenetics and expression of key genes associated with cardiac fibrosis: NLRP3, MMP2, MMP9, CCN2/CTGF and AGT

Aims:

Excessive inflammatory signaling and pathological remodeling of the extracellular matrix drive cardiac fibrosis and require changes in gene expression.

Materials and methods:

Using bioinformatics, both tissue-specific expression profiles and epigenomic profiles of some genes critical for cardiac fibrosis were examined, namely, NLRP3, MMP2, MMP9, CCN2/CTGF, AGT (encodes angiotensin II precursors) and hsa-mir-223 (post-transcriptionally regulates NLRP3).

Results:

In monocytes, neutrophils, fibroblasts, venous cells, liver and brain, enhancers or super-enhancers were found that correlate with high expression of these genes. One enhancer extended into a silent gene neighbor. These enhancers harbored tissue-specific foci of DNA hypomethylation, open chromatin and transcription factor binding.

Conclusions:

This study identified previously undescribed enhancers containing hypomethylated transcription factor binding subregions that are predicted to regulate expression of these cardiac fibrosis-inducing genes.

MEF-2 isoforms' (A-D) roles in development and tumorigenesis

Myocyte enhancer factor (MEF)-2 plays a critical role in proliferation, differentiation, and development of various cell types in a tissue specific manner. Four isoforms of MEF-2 (A-D) differentially participate in controlling the cell fate during the developmental phases of cardiac, muscle, vascular, immune and skeletal systems. Through their associations with various cellular factors MEF-2 isoforms can trigger alterations in complex protein networks and modulate various stages of cellular differentiation, proliferation, survival and apoptosis. The role of the MEF-2 family of transcription factors in the development has been investigated in various cell types, and the evolving alterations in this family of transcription factors have resulted in a diverse and wide spectrum of disease phenotypes, ranging from cancer to infection. This review provides a comprehensive account on MEF-2 isoforms (A-D) from their respective localization, signaling, role in development and tumorigenesis as well as their association with histone deacetylases (HDACs), which can be exploited for therapeutic intervention.

Differentially Tolerized Mouse Antigen Presenting Cells Share a Common miRNA Signature Including Enhanced mmu-miR-223-3p Expression Which Is Sufficient to Imprint a Protolerogenic State

Dendritic cells (DCs) are pivotal for the induction and maintenance of antigen-specific tolerance and immunity. miRNAs mediate post-transcriptional gene regulation and control in part the differentiation and stimulation-induced immunogenic function of DCs. However, the relevance of miRNAs for the induction and maintenance of a tolerogenic state of DCs has scarcely been highlighted yet. We differentiated mouse bone marrow cells to conventional/myeloid DCs or to tolerogenic antigen presenting cells (APCs) by using a glucocorticoid (dexamethasone) or interleukin-10, and assessed the miRNA expression patterns of unstimulated and LPS-stimulated cell populations by array analysis and QPCR. Differentially tolerized mouse APCs convergingly down-regulated a set of miRNA species at either state of activation as compared with the corresponding control DC population (mmu-miR-9-5p, mmu-miR-9-3p, mmu-miR-155-5p). These miRNAs were also upregulated in control DCs in response to stimulation. In contrast, miRNAs that were convergingly upregulated in both tolerized APC groups at stimulated state (mmu-miR-223-3p, mmu-miR-1224-5p) were downregulated in control DCs in response to stimulation. Overexpression of mmu-miR-223-3p in DCs was sufficient to prevent stimulation-associated acquisition of potent T cell stimulatory capacity. Overexpression of mmu-miR-223-3p in a DC line resulted in attenuated expression of known (Cflar, Rasa1, Ras) mRNA targets of this miRNA species shown to affect pathways that control DC activation. Taken together, we identified sets of miRNAs convergingly regulated in differentially tolerized APCs, which may contribute to imprint stimulation-resistant tolerogenic function as demonstrated for mmu-miR-223-3p. Knowledge of miRNAs with protolerogenic function enables immunotherapeutic approaches aimed to modulate immune responses by regulating miRNA expression.

C/EBPα overrides epigenetic reprogramming by oncogenic transcription factors in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous disease caused by recurrent mutations in the transcription regulatory machinery, resulting in abnormal growth and a block in differentiation. One type of recurrent mutations affects RUNX1, which is subject to mutations and translocations, the latter giving rise to fusion proteins with aberrant transcriptional activities. We recently compared the mechanism by which the products of the t(8;21) and the t(3;21) translocation RUNX1-ETO and RUNX1-EVI1 reprogram the epigenome. We demonstrated that a main component of the block in differentiation in both types of AML is direct repression of the gene encoding the myeloid regulator C/EBPα by both fusion proteins. Here, we examined at the global level whether C/EBPα is able to reverse aberrant chromatin programming in t(8;21) and t(3;21) AML. C/EBPα overexpression does not change oncoprotein expression or globally displace these proteins from their binding sites. Instead, it upregulates a core set of common target genes important for myeloid differentiation and represses genes regulating leukemia maintenance. This study, therefore, identifies common CEBPA-regulated pathways as targets for therapeutic intervention.